The present invention relates to printers and, more specifically, to a mechanical arrangement for automatically displacing a roller from a platen upon opening a printer head pressure plate. The automatic displacement feature facilitates the loading of stock (e.g., label stock) in the printer. Other aspects of the invention include the ability of the printer to be readily and easily reconfigured to accommodate an optional thermal ribbon cartridge and a variety of thermal print mechanisms.
Thermal printers are used increasingly in retail, warehouse, and other locations to generate adhesive labels for marking goods to facilitate identification, tracking, and pricing. Due to the print quality, accuracy, and versatility of dot matrix or array type thermal print mechanisms, a wide variety of information can be produced quickly and inexpensively on the labels as the need arises. Lot sizes of labels can be as small as one or as large as several hundred or more, depending upon the particular application. Printer electronics integral with the printer may include a microprocessor, memory, and associated internal and external communications so that the printer can be used to create alphanumeric characters of varying size, font, and orientation, stylized graphical markings such as logotypes and trademarks, and machine readable indicia such as bar codes for the particular goods to be labeled. A variety of these characters, markings, and indicia can be printed in combination on a single label.
Thermal printers can print on thermal paper which darkens or changes color when heated above a threshold temperature by the thermal print mechanism or printer head. By selectively activating discrete thermal elements in the printer head array as the thermal paper passes by, the desired information can be reproduced on the thermal paper. To provide intimate, uniform contact between the printer head and the label, the label is passed typically through a nip formed by the printer head and a powered rubber platen roller. The platen may be used to drive the label through the nip. Instead of heating the label, a thermal transfer ribbon having a layer of dried ink on a thin backing sheet can be disposed between the printer head and a paper label on the platen. As the printer head is heated above the ribbon ink threshold temperature, the ink melts and is transferred to the label where it dries and forms an indelible marking of the desired information.
xe2x80x9cLabel stockxe2x80x9d generally includes a series of printable surfaces of paper or other label material adhesively and releasably attached to a web carrier backing. The label stock typically is manufactured in roll form for continuous feeding through a thermal printer. xe2x80x9cLinerlessxe2x80x9d label stock is also commercially available which is in the form of a roll of continuous adhesive strip. Special handling of this stock is required to prevent misfeeding and jamming of the thermal printer. For example, a silicone platen roller may be used to prevent adhesion of the stock thereto and a cutter mechanism may be provided to separate a printed label portion from the remaining roll.
In printers for printing on a series of labels adhered to a web, it may be desirable to dispense printed labels individually, wholly or partially delaminated from the web, to facilitate removal by an operator. By passing the web across a peeler bar at an acute angle after discharge from the nip formed between the printer head and platen, a leading edge of the label becomes delaminated or detached from the web. An additional roller may be provided biased against the platen or other roller to form a second nip through which solely the web passes. By keeping the web taut and maintaining close conformance of the web to the peeler bar, reliable dispensing of the printed labels may be ensured.
When initially threading the printer with the label stock, the stock must be passed through the printer head nip and, if the peeler bar is to be used, the web also must be passed through the roller nip. The web should be taut between the printer head nip and the roller nip to tightly conform the web to the peeler bar. Various arrangements are known for providing a gap between the printer head and platen to facilitate loading. For example, see U.S. Pat. Nos. 5,014,073 and 5,150,130. Known arrangements for providing a gap between a roller and a platen to facilitate removal of paper jams include the arrangement disclosed in U.S. Pat. No. 4,947,185. Arrangements that require manual actuation to provide a gap between the roller and the platen include a spring loaded roller with bi-stable positioning so that the roller is stable in positions both against the platen as well as spaced therefrom. Manual actuation is required both to displace the roller from the platen as well as return the roller to the contact position. Each of these arrangements entails separate apparatus for displacing a printer head and a roller from the platen.
It is an object of the invention to provide a printer which has an improved stock (e.g., label stock) loading feature.
It is another object of the invention to provide a printer that is readily and easily reconfigurable to accommodate an optional thermal ribbon cartridge and a variety of thermal print mechanisms.
An improved printer and printer subassembly according to the invention are useful in a wide variety of applications including, but not limited to, thermal printing on label stock. The printer subassembly includes a powered platen having an axis of rotation. A thermal print mechanism, including a printer head, is aligned with and biased against the platen by a stacked assembly of a pressure plate and an alignment plate with springs disposed therebetween. The printer head is fixedly mounted on the alignment plate which is supported by the pressure plate using a pivot feature in combination with a centering feature ensuring proper alignment of the printer head relative to the platen.
The pressure plate is hinged about an axis along an edge perpendicular to the platen axis. A latch disposed along an opposite edge of the pressure plate maintains the plate in a closed position for printing. The latch may include a microswitch to signal a printer controller that the pressure plate is closed and printing can begin if the printer is otherwise ready. Releasing the latch permits the pressure plate to be swung open providing access to load label stock as well as clean or remove the printer head.
The pressure plate includes an actuation mechanism proximate the hinge axis which cooperates with a follower. The follower is coupled to a roller biased against the platen to effect translation of the roller as the follower is moved. The actuation mechanism may be a cam sector with a fixed radial dimension and a varying axial dimension. The follower may be a cantilevered arm with a pin for sliding contact on the sector. As the pressure plate is moved from a closed to an open position, the follower pin slides along the contoured surface of the cam sector, translating the roller from a position biased against the platen to a position spaced therefrom. Accordingly, with the pressure plate in an open position, a gap is formed between the roller and the platen. After passing the label stock over the platen and a peeler bar, the web may be passed through the gap and held taut. As the pressure plate is closed and latched, the label stock is captured between the printer head and the platen and the web is captured between the roller and the platen. The label stock may then be advanced automatically or manually to align a leading edge of a label with the printer head for printing.
A detent in the cam sector corresponding to a fully open position of the pressure plate may be provided for engagement with the follower pin to keep the pressure plate in the open position during label stock loading. To provide parallel translation of the roller relative to the platen, cam surfaces may be affixed to both ends of the roller. The follower may also include an optional extension for manual translation of the roller when the pressure plate remains in a closed position. A frame supporting the roller may include slots to limit manual translation of the roller within predetermined limits.
The modular design of the interface between the pressure plate and the alignment plate permits rapid manual replacement or swapping of thermal print mechanisms without the need for tools. Additionally, the printer may include an optional modular thermal transfer ribbon assembly for printing on plain paper labels.
The printer may also be provided with electronics reconfigurable to accommodate a variety of thermal print mechanisms and the optional thermal transfer ribbon. Configuration information may be stored in memory, read by a microprocessor, and used to configure a programmable device such a field programmable gate array (xe2x80x9cFPGAxe2x80x9d) to allow print data received by the microprocessor to pass through the FPGA and be printed by the print mechanism loading in the printer. Configuration information may include parameters such as printer model, which includes motor type and printer head type.
According to the invention, loading of stock is greatly facilitated. Further, the printer is readily reconfigurable to accommodate an optional thermal ribbon cartridge and a variety of thermal print mechanisms which are easily removed and replaced without the need for tools or special alignment techniques.